Platinum and titanium containing electrocatalysts

ABSTRACT

The present teachings are directed toward electrocatalyst compositions of platinum, titanium and at least a third metal for use in fuel cells. The electrocatalyst composition is composed essentially of platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and at least a third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal can be at least one member selected from the group consisting of nickel, vanadium and molybdenum.

BACKGROUND

1. Field of the Invention

The present teachings relate to electrocatalyst compositions composed essentially of platinum, titanium and a third metal, with platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal is at least one member selected from the group consisting of nickel, vanadium and molybdenum.

2. Discussion of the Related Art

The desire to reduce the amount of expensive platinum group metals needed to obtain a desired level of performance for an electrocatalyst is an ever present operational parameter for the design of many devices and procedures involving electrocatalysts.

Enhancement of catalytic performance by combining platinum with various less expensive metals is one of the possible avenues to either reduce the amount of platinum required, or perhaps increase the efficiency of the catalyzed reaction, or both. One application of interest for Pt-based electrocatalyst is, for instance, the cathode reaction of a typical proton exchange membrane fuel cell (“PEMFC”) which can utilize an electrode containing a Pt-based electrocatalyst to catalyze the oxygen reduction reaction.

A need exists for electrocatalyst compositions and thin film fuel cell electrocatalysts that reduce the amount of platinum needed to achieve a desired performance level.

SUMMARY

The present teachings satisfy the need for electrocatalyst compositions with lower platinum amounts, particularly for fuel cell electrocatalysts, and especially for thin film fuel cell electrocatalysts.

An electrocatalyst composition including a metal composition composed essentially of platinum, titanium and a third metal is taught by the present disclosure. The composition can contain platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal is at least one member selected from the group consisting of nickel, vanadium and molybdenum.

A fuel cell electrocatalyst comprising a composition containing essentially platinum, titanium and a third metal is also taught by the present disclosure. The composition can contain platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, a third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal is at least one member selected from the group consisting of nickel, vanadium and molybdenum.

The present teachings further include a fuel cell assembly comprising at least one thin film electrocatalyst, a membrane, and at least one electrode. The thin film electrocatalyst comprises a composition composed essentially of platinum, titanium and a third metal taught by the present disclosure. The composition can contain platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent and a third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal is at least one member selected from the group consisting of nickel, vanadium and molybdenum. The thin film electrocatalyst can also be a supported electrocatalyst which can comprise a powder composition composed essentially of platinum, titanium and a third metal supported on a high surface area support material. The electrocatalyst can be a supported nanoparticle-containing powder.

DETAILED DESCRIPTION

The present teachings relate to an electrocatalyst composition including a metal composition composed essentially of platinum, titanium and a third metal. The composition can contain platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal is at least one member selected from the group consisting of nickel, vanadium and molybdenum.

An additional embodiment of the electrocatalyst composition can have platinum present in an atomic percentage ranging between about 60 percent and about 80 percent, titanium present in an atomic percentage ranging between about 5 percent and about 25 percent, and the third metal present in an atomic percentage ranging between about 5 percent and about 25 percent. Yet another example of the electrocatalyst composition can have platinum present in an atomic percentage ranging between about 60 percent and about 70 percent, titanium present in an atomic percentage ranging between about 10 percent and about 20 percent, and the third metal present in an atomic percentage ranging between about 10 percent and about 20 percent. A further additional embodiment of the electrocatalyst composition can have platinum present in an atomic percentage ranging between about 60 percent and about 80 percent, titanium present in an atomic percentage ranging between about 5 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 25 percent. Another example of the electrocatalyst composition can have platinum present in an atomic percentage ranging between about 60 percent and about 70 percent, titanium present in an atomic percentage ranging between about 10 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 20 percent.

Other electrocatalyst compositions taught by the present disclosure can have platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and nickel, vanadium, or molybdenum as a third metal present at atomic percentages ranging between about 10 percent and about 20 percent. Additional electrocatalyst compositions taught by the present disclosure can have platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and nickel, vanadium, or molybdenum as a third metal present at atomic percentages ranging between about 1 percent and about 20 percent.

The electrocatalyst can be a supported nanoparticle-containing powder. The nanoparticles present in the supported powder can range in size from about 0.5 nm to about 100 nm, and can be composed of platinum, titanium, and one of nickel, vanadium or molybdenum.

Also provided by the present teachings is a fuel cell electrocatalyst composed from an electrocatalyst composition, where the composition is composed essentially of platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and a third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal is at least one member selected from the group consisting of nickel, vanadium and molybdenum.

The fuel cell electrocatalyst can be a supported nanoparticle-containing powder. The nanoparticles present in the supported powder can range in size from about 0.5 nm to about 100 nm, and can be composed of a composition composed essentially of platinum, titanium, and a third metal. The nanoparticle powder composition can be composed of platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal can be at least one member selected from the group consisting of nickel, vanadium and molybdenum.

The fuel cell electrocatalyst can be in various forms, including, for example, a thin film, a supported powder, or a supported nanoparticle-containing powder. The nanoparticle-containing fuel cell electrocatalyst can be supported on a support, such as a high surface area carbon, like carbon black, for instance, or can be unsupported.

The fuel cell electrocatalyst can be prepared by, for example, physical vapor deposition. The physical vapor can be plasma generated by a suitable means, for example, plasma guns. Further examples of deposition methods include, for instance, ion plating, ion implantation, evaporation, and laser surface alloying.

The fuel cell electrocatalyst can be prepared by, for example, simultaneous deposition of the platinum metal, the titanium metal and the third metal. Alternatively, the fuel cell electrocatalyst as a thin film can be prepared by sequential deposition of the various metals, or by various combinations of simultaneous and sequential deposition of the various metals present in the electrocatalyst composition.

A fuel cell assembly including a membrane, a thin film, or supported, electrocatalyst, and an electrode which can be different from the thin film electrocatalyst is provided. The thin film, or supported, electrocatalyst can be composed of a composition composed essentially of platinum, titanium, and a third metal. The composition can have platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 30 percent. The third metal can be at least one member selected from the group consisting of nickel, vanadium and molybdenum.

In additional embodiments of the present fuel cell assembly, the platinum can be present in an atomic percentage ranging between about 60 percent and about 80 percent, titanium in an atomic percentage ranging between about 5 percent and about 25 percent, and the third metal in an atomic percentage ranging between about 5 percent and about 25 percent. Further additional embodiments of the present fuel cell assembly can have platinum present in an atomic percentage ranging between about 60 percent and about 80 percent, titanium present in an atomic percentage ranging between about 5 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 25 percent.

Other examples of the present fuel cell assembly can have platinum present in an atomic percentage ranging between about 60 percent and about 70 percent, titanium present in an atomic percentage ranging between about 10 percent and about 20 percent, and the third metal present in an atomic percentage ranging between about 10 percent and about 20 percent. Still further examples of the present fuel cell assembly can have platinum present in an atomic percentage ranging between about 60 percent and about 70 percent, titanium present in an atomic percentage ranging between about 10 percent and about 30 percent, and the third metal present in an atomic percentage ranging between about 1 percent and about 20 percent.

Yet other examples of the present fuel cell assembly can have an electrocatalyst composed of a composition composed essentially of platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and nickel, vanadium, or molybdenum as a third metal present at atomic percentages ranging between about 10 percent and about 20 percent. Further embodiments of the present fuel cell assembly can have an electrocatalyst composed of a composition composed essentially of platinum present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium present in an atomic percentage ranging between about 1 percent and about 30 percent, and nickel, vanadium, or molybdenum as a third metal present at atomic percentages ranging between about 1 percent and about 20 percent.

The supported electrocatalyst can be composed of a powder composition. The powder composition can be prepared by any suitable preparation method, for instance, wet chemical methods. The powder can be supported on a suitable high surface area support. The high surface area support can be, for instance, carbon or alumina. High surface area refers to supports with surface areas of at least about 100 m²/g.

For all of the compositions taught herein, the concentrations of the metals present therein can be varied to optimize the performance of the electrocatalyst. The composition can be varied dependent on such factors as the operating environment and performance requirements. The composition can, in some embodiments, include platinum present in an atomic percentage ranging between about 60 percent and about 80 percent, or in an atomic percentage ranging between about 60 percent and about 70 percent.

Additionally, the composition can, in some embodiments, include titanium present in an atomic percentage ranging between about 5 percent and about 25 percent, in an atomic percentage ranging between about 10 percent and about 20 percent, in an atomic percentage ranging between about 5 percent and about 30 percent, or in an atomic percentage ranging between about 10 percent and about 30 percent. Furthermore, the composition can, in some embodiments, include nickel present in an atomic percentage ranging between about 1 percent and about 25 percent, between about 5 percent and about 25 percent, between about 10 percent and about 20 percent, or between about 1 percent and about 20 percent, or molybdenum present in an atomic percentage ranging between about 1 percent and about 25 percent, between about 5 percent and about 25 percent, between about 10 percent and about 20 percent, or between about 1 percent and about 20 percent, or vanadium present in an atomic percentage ranging between about 1 percent and about 25 percent, between about 5 percent and about 25 percent, between about 10 percent and about 20 percent, or between about 1 percent and about 20 percent.

The thin film electrocatalyst can be the cathode of a PEMFC and can drive the oxygen reduction reaction of the PEMFC.

A thin film can be a film ranging in thickness from nanometers to micrometers thick and can be prepared by physical vapor deposition, electrochemical plating, or ink coating of the desired components onto a suitable substrate. One possible means of producing the desired thin film is physical vapor deposition. Physical vapor deposition refers to the deposition of the components from component vapors generated through, for instance, heat, plasma, and electron beams. The deposition of the components, in this case, platinum, titanium and additional metals, can occur simultaneously, or sequentially. A suitable preparation method is described in pending U.S. patent application Ser. No. 10/757,302 filed Jan. 14, 2004.

The metals in the electrocatalyst composition can be present in any of several possible oxidation states and structures. The metal oxidation state and structure depend on a number of factors, including, for example, the chemical formulation, heat treatment, and any exposure to hydrogen and/or oxygen-containing environments. The possible metal structures can include, for example, alloys, mixed oxides, hydrous oxides, mixed hydrides, bronzes, pervoskites, and so forth. The structure of any metals on the surface of the electrocatalyst can differ from, or can be the same as, the structure of metals located within the bulk of the electrocatalyst. The concentration of any metals on the surface of the electrocatalyst can differ from, or can be the same as, the concentration of metals located within the bulk of the electrocatalyst.

The metal components of the composition can be present at or on the surface of the electrocatalyst. The metal components, both oxidized and metallic, can be located anywhere in the structure of an electrocatalyst composition according to the present teachings.

The atomic percentages set forth herein were determined by EDX analysis of the thin film electrocatalyst compositions after evaluation by rotating disc electrode as detailed in the Example section below.

All publications, articles, papers, patents, patent publications, and other references cited herein are hereby incorporated herein in their entireties for all purposes.

Although the foregoing description is directed to the preferred embodiments of the present teachings, it is noted that other variations and modifications will be apparent to those skilled in the art, and which may be made without departing from the spirit or scope of the present teachings.

The following examples are presented to provide a more complete understanding of the present teachings. The specific techniques, conditions, materials, and reported data set forth to illustrate the principles of the present teachings are exemplary and should not be construed as limiting the scope of the present teachings.

EXAMPLES

Thin film samples of varying platinum, titanium and additional metals composition were prepared by physical vapor deposition of plasma generated metal vapors. A suitable preparation method is described in pending U.S. patent application Ser. No. 10/757,302 filed Jan. 14, 2004.

The activity levels for the oxygen reduction reaction of the platinum, titanium and additional metal-containing electrocatalysts were electrochemically screened using a hydrodynamic rotating disc electrode (RDE) apparatus, which is capable of screening numerous material compositions simultaneously. A suitable screening method is described in pending U.S. patent application Ser. No. 10/713,242 filed Nov. 14, 2003.

Thin film samples were coated onto 5 mm diameter glassy carbon electrodes. Following electrochemical cleaning, the samples were then used as the working electrodes in oxygen reduction reaction cells, and the results are presented in Table 1 below.

In Table 1, the atomic percentages of the platinum, titanium and third metal components are tabulated. The shifts of half wave potential (ΔE_(1/2)) in mV are presented, along with the platinum mass-fraction-based activity relative to pure platinum thin film (R-Act) at both 0.7 V and 0.8 V for each sample, in Table 1.

TABLE 1 COMPOSITION Pt Ti Ni Mo V ΔE_(1/2) R-Act R-Act (at %) (at %) (at %) (at %) (at %) (mV) (0.7 V) (0.8 V) 0.79 0.09 0.11 36.1 2.2 2.3 0.77 0.08 0.14 17.7 1.7 1.6 0.73 0.09 0.18 55.4 3.0 3.7 0.69 0.09 0.23 67.4 4.0 4.7 0.75 0.13 0.12 48.3 2.8 3.2 0.72 0.13 0.15 55.8 2.7 4.1 0.68 0.12 0.20 70.0 3.4 5.3 0.64 0.12 0.23 91.5 5.8 8.0 0.72 0.17 0.11 59.2 3.1 3.9 0.67 0.17 0.16 69.5 4.0 5.0 0.63 0.17 0.20 78.5 4.7 6.4 0.60 0.17 0.22 91.4 7.1 9.0 0.66 0.21 0.12 66.4 3.8 4.7 0.63 0.21 0.16 83.2 5.2 7.1 0.58 0.22 0.21 79.6 5.7 6.8 1.00 0.00 0.00 0.0 1.0 1.0 0.82 0.10 0.08 25.6 1.7 1.9 0.75 0.06 0.18 41.7 2.0 2.8 0.72 0.07 0.20 53.2 2.5 3.7 0.77 0.14 0.08 28.9 1.8 2.2 0.71 0.14 0.16 52.0 2.5 3.5 0.66 0.14 0.20 61.4 2.9 4.4 0.73 0.18 0.09 32.0 1.9 2.2 0.69 0.18 0.14 44.7 2.4 3.0 0.65 0.19 0.16 48.1 2.7 3.3 0.61 0.18 0.21 55.2 3.2 4.0 0.66 0.24 0.09 33.3 2.1 2.3 0.63 0.23 0.13 14.8 1.6 1.4 0.58 0.25 0.17 2.3 1.4 1.3 0.65 0.14 0.22 73.6 3.5 5.7 0.62 0.18 0.20 61.4 3.7 4.5 0.70 0.13 0.17 54.7 2.6 3.7 0.74 0.10 0.16 46.0 2.3 3.2 0.80 0.10 0.10 16.0 1.4 1.4 0.75 0.10 0.15 37.0 2.1 2.3 0.70 0.10 0.20 55.3 2.8 3.4 0.68 0.09 0.23 74.8 4.0 5.2 0.76 0.14 0.10 29.1 1.9 1.9 0.70 0.15 0.15 44.4 2.4 2.7 0.67 0.14 0.19 60.9 3.5 3.9 0.70 0.11 0.19 88.3 7.0 7.6 0.73 0.18 0.09 43.5 2.7 2.6 0.68 0.18 0.14 −90.9 0.3 0.7 0.64 0.17 0.19 51.2 3.5 3.1 0.69 0.13 0.18 88.4 7.9 7.8 0.66 0.24 0.10 21.6 2.0 1.5 0.62 0.24 0.14 33.1 2.7 2.0

The foregoing detailed description of the various embodiments of the present teachings has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present teachings to the precise embodiments disclosed. Many modifications and variations will be apparent to practitioners skilled in this art. The embodiments were chosen and described in order to best explain the principles of the present teachings and their practical application, thereby enabling others skilled in the art to understand the present teachings for various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the present teachings be defined by the following claims and their equivalents. 

1. A fuel cell assembly comprising: a cathode, a membrane, and an anode; wherein the cathode comprises a composition consisting essentially of platinum, titanium, and a third metal, wherein platinum is present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium is present in an atomic percentage ranging between about 1 percent and about 30 percent, and the third metal is present in an atomic percentage ranging between about 1 percent and about 30 percent, wherein the third metal is vanadium, and wherein the fuel cell assembly consists of a proton exchange membrane fuel cell assembly.
 2. The fuel cell assembly according to claim 1, wherein platinum is present in an atomic percentage ranging between about 60 percent and about 80 percent, titanium is present in an atomic percentage ranging between about 5 percent and about 9 percent, and the third metal is present in an atomic percentage ranging between about 1 percent and about 25 percent.
 3. The fuel cell assembly according to claim 1, wherein platinum is present in an atomic percentage ranging between about 60 percent and about 70 percent, titanium is present in an atomic percentage ranging between about 10 percent and about 30 percent, and the third metal is present in an atomic percentage ranging between about 1 percent and about 20 percent.
 4. The fuel cell assembly according to claim 2, wherein the third metal is vanadium and is present in an atomic percentage ranging between about 1 percent and about 20 percent.
 5. The fuel cell assembly according to claim 1, wherein the electrocatalyst comprises a thin film electrocatalyst.
 6. The fuel cell assembly according to claim 1, wherein the electrocatalyst comprises a supported nanoparticle-containing powder electrocatalyst.
 7. A fuel cell assembly comprising: a cathode, a membrane, and an anode; wherein the cathode consists essentially of platinum, titanium, and vanadium, wherein platinum is present in an atomic percentage ranging between about 55 percent and about 85 percent, titanium is present in an atomic percentage ranging between about 1 percent and about 30 percent, and vanadium is present in an atomic percentage ranging between about 1 percent and about 30 percent.
 8. The fuel cell assembly according to claim 7, wherein the vanadium is present in an atomic percentage ranging between about 10 percent and about 20 percent.
 9. The fuel cell assembly according to claim 7, wherein the vanadium is present in an atomic percentage ranging between about 1 percent and about 20 percent. 